Process for preparing alkali metal greases



Patented Jan. 27, 1953 PROCESS FOR. PREPARING ALKALI METAL GREASES JohnP. Dilworth, Fishkill, George W. Eckert, Glenham, and William J. Coppoc,Beacon, N. Y., assignors to The Texas Company, New York, N. Y., acorporation of Delaware N Drawing. Application October 26, 1950, SerialNo. 192,376

12 Claims. 1

This invention relates to a novel procedure for preparing alkali metalgreases. More particularly, this invention relates to a procedurewhereby alkali metal greases of high dropping point and of outstandingperformance over a wide temperature range are prepared.

Alkali metal greases characterized by high dropping point and excellentperformance characteristics over a wide temperature range are preparedby the novel process of this invention involving saponification of amixture of mineral oil, alkali metal hydroxide and a soap-formingmaterial which is either a soap-forming fatty acid, a soap-forming esteror a mixture of soapforming fatty acids and esters, dehydration of thesaponified mixture and digestion of the saponifled, dehydrated reactionmixture in a pressure kettle under an air pressure of 50 to 120 poundsper square inch and at a temperature of 300 to 390 F. for a period of atleast five hours. The reaction mixture contains excess alkali metalhydroxide over the stoichiometric amount required to saponify thesoap-forming constituents of the reaction mass. The excess alkali metalhydroxide amounts to 1 to 3 per cent of the final composition of thegrease. Digestion of the saponified, dehydrated reaction mixture in apressure kettle under an air pressure of 50 to 120 pounds per squareinch and a temperature of 300 to 390 F. results in partial oxidation ofthe reaction mixture to form acidic materials which are neutralized bythe excess alkali present. The alkali metal greases produced by thisinvention are characterized by dropping points over 500 F. and possessgood low temperature torque properties so that they are properlyclassified as wide temperature range ball and roller bearing greases.

It has been known in the grease making art to employ mineral oilsandsoap-forming materials which have been preoxidized either alone or incombination prior tothe addition of caustic in the grease formulation.Greases prepared from pre-oxidlzed mineral oils and soap-formingmaterials are hard block-type greases which are known as driving journalgreases. It has also been known to effect saponification of the greasemaking ingredients in a, pressure kettle under air pressure. The processof this invention distin guishes from the prior known procedures formanufacturing grease in that a, saponified and dehydrated reactionmixture is digested in a pressure kettle at an elevated temperatureunder super-atmospheric air pressure. Moreover, none of the proceduresof the prior art involving pressure kettle treatment of one or more ofthe grease ingredients produces alkali metal greases which arecharacterized by very high dropping points and good low temperaturetorque properties. For example, a buttery-type sodium grease with adropping point over 500 F. is pre pared by the procedure of thisinvention. The preparation of alkali metal greases characterized by widetemperature range properties represents a significant advance in the artof grease making.

Naphthene base oils or parafiin base oils can be employed in the processof this invention to prepare novel alkali metal greases. With theparaffin base oils it is necessary to incorporate petroleum mahoganysulfonate salts as stabilizing agents in order to obtain suitablegreases. Sodium petroleum mahogany sulfonate is ordinarily employed asthe stabilizing agent. With parafiin base oils, the added petroleummahogany sulfonat-e salt amounts to about 0.24 to 4 per cent of thefinal calculated grease composition. The sodium petroleum mahoganysulfonate is added to the reaction mixture together with the paraifinbase oil and is present during saponification and dehydration of thereaction mixture.

, When naphthene base oils, commonly known as pale oils, are employed inthe process of this invention, it is not necessary to employ stabilizingagents such as petroleum mahogany sulfonate salts since greases of highstability are prepared without the use of a stabilizing agent.

The grease making process of the invention can be used with almost anytype of soap-forming material, but best results are obtained withsoap-forming acids, esters and mixtures thereof which contain aconsiderable olefin content. The presence of double bonds insoap-forming materials providespoints of attack for the oxidation whichoccurs during-the high temperaturepressure digestion of the saponified,dehydrated reaction mixture. Soap-forming fatty acids, soap-formingesters and-mixtures thereof may all be employed in this invention withspecial emphasis being placedon the use of a soapforming stock, whichisolefinic in nature and has an iodine number higher than 40.

A particularly preferred soap-forming material comprises a' mixture ofmenhaden oil and hydrogenated fishoil fatty was commercially known asSnodotte acids. A 3 to 1 menhaden oil-Snodotte acid mixture has provenparticularly useful in the process of this invention.

Commercially available Snodotte acids have approximately the followingstated compositions:

Per cent Myristic acid 9 Palmitic 22 Stearic 2'7 Arachidic 22 BehenicTypical tests on commercially available Snoclotte acids are as follows:

Sap. No 197 Neut. No 193 Iodine l Titer, "C 54.6

Other unsaturated soap-forming acids and esters such as caster oil,linoleic and linolenic acids are also useful in the process of thisinvention. Advantageously, the soap-forming material has an iodinenumber higher than 90.

The excess alkali metal hydroxide employed in procedures of thisinvention amounts to approximately 1 to 3 per cent of the finalcalculated composition of the grease. Advantageously, the stoichiometricquantities of caustic and a major portion of the excess caustic is addedto the grease mixture prior to saponification and the remain ing causticsolution constituting a minor portion of the excess alkali metalhydroxide is added after the elevated temperature-air pressure digestionof the saponified, dehydrated grease mixture. It is also possible to addthe total caustic during the saponification of the grease mixture. Inthe preferred procedure, the stoichiometric caustic plus more than half,and preferably 70 to 90 per cent, of the excess caustic are added priorto saponification; remaining excess caustic is added after the hightemperature-air pressure digestion.

All alkali metal greases may be prepared in accordance with theprocedure of this invention, but the procedure is particularly adaptedto sodium and lithium greases. Alkali metal hydroxide is advantageouslyadded to the reaction mixture in the form of a saturated aqueoussolution. The procedur of the invention constitutes the preparation of abuttery-type sodium base grease.

Various additives are blended into the grease after the digestion of thesaponified, dehydrated mixture at a temperature of 300 to 390 F. and atan air pressure of 50 to 120 pounds per square inch. For example,diphenylamine, an oxidation inhibitor, may be blended into the grease ata temperature of about 250 F. and atmospheric conditions during thecooling of the grease after elevated temperature-pressure digestion.Aluminum stearate may also be added to the grease to impart waterresistance during the cooling of the grease.

The saponification procedure: employed in this invention is effected atconventional conditions. The mineral lubricating oil fraction and thesoapforming stock are heated with stirring to a temperature ofapproximately 125 to 160 F. to effect good distribution of the reagents.If a parailin base mineral oil is employed, the stabilizing petroleummahogany sulfonate salt is. added to the mixture at this time. Atapproximately 150 F. the aqueous solution of alkali metal hydroxide isadded to the reactionmixture. A small amount of silicone anti-foamagent; is advantageously added together with the caustic solution tominimize foaming. The saponification is effected at a temperaturebetween 150 and 200 F. period of about one hour.

Dehydration of the saponified reaction mixture is effected at atemperature between about 290 and 350 F. and ordinarily takesapproximately 3 to 5 hours. The preferred temperature range fordehydrating the saponified reaction mass is 300 to 330 F.

Digestion of the saponified and dehydrated reaction mixture atsuperatmospheric pressure is effected in a closed vessel or autoclavewhich is equipped with efiicient stirring means. It is recommended thatthe kettle wherein the reaction mixture is digested under air pressurebe equipped with side wall scrapers.

The air pressure in the closed kettle is maintained between and 120pounds per square inch and advantageously at a pressure of to pounds persquare inch. The temperature during pressurized digestion of thereaction mixture is maintained between 300 and 390 F. and preferably ata temperature of 340 to 365 F. The period of time required for thepressure kettle digestion of the reaction mixture varies with thetemperature and pressure conditions employed during the oxidativedigestion but ordinarily will be in the range of 5 to 15 hours.

The nature of the soap-forming material employed is a decisive factor indetermining the temperature and pressure conditions to be employed andthe length of time required to obtain the product of the desiredcharacteristics. With highly olefinie stocks, temperatures and pressuresin the lower portion of the prescribed range are employed and durationof the pressurized digestion is also within the lower portion of theprescribed range. In contrast, when highly parafiinic soap-formingmaterials such as tallow are employed, higher temperatures and pressureswithin the prescribed ranges are employed and, in addition, pressurizeddigestion is continued for a longer time.

After the pressurized digestion, additives such as aluminum stearate anddiphenylamine are added While the reaction mixture is hot. The additivesare usually added at temperatures between 275 and 380 F. The remainingexcess alkali is also added during the cooling procedure if splitaddition of excess alkali is employed. Addition of residual excessalkali is advantageously effected during cooling of the grease at atemperature of about 275 to 300 F.

The grease is drawn at a temperature of about 200 F. Advantageously itis screened through 60 mesh screens during the drawing operations.

The novel grease making process of this invention is illustrated inExamples I and II wherein sodium base and lithium base greases areprepared in accordance with the procedure of this invention.

ina

Emamplc I A mixture of 40.3 pounds of a paraflinic mineral lubricatingoil fraction having an SAE viscosity of about 20, 0.9 pound of sodium,petroleum mahogany sulfonate and 11.6 pounds of a 3 to 1 mixture ofmenhaden oil-Snodotte acids were charged to a kettle. This mixture washeated to F. and 6 g. of a methyl silicone (Dow-Corning Anti-Foam A)were added. At 150 F. 5.54 pounds of 49.3 per cent solution of sodiumhydroxide were added to the reaction mixture; the added causticcomprised the stoichiometric amount required to saponify thesoap-forming constitu nts and in addition an excess of sodium hydroxidewhich calculated approximately 1.9 weight per cent of the finalcalculated grease composition. The reaction mixture was stirred in thekettle at a temperature of 150 to 200 F. for approximately 1 hour withthe resulting saponifioation of the soap-forming materials present inthe reaction mass. The reaction mixture was then raised to a temperatureof 300 to 330 F. and maintained at this level for approximately 3 hourswith the resulting dehydration of the reaction mixture. Afterdehydration the head was placed on the pressure kettle and thetemperatur raised to approximately 340 F. whereupon the pressure kettlewas subjected to an air pressure of '70 to 90 pounds per square inch.The reaction mixture was stirred in the pressure kettle at a temperatureof 340 to 350 F. and under an air pressure of 70 to 90 pounds per squareinch for approximately 12 hours. At the end of this time the airpressure was shut off, the head removed from the kettle and 2.84 poundsof aluminum stearate added, whereafter the mixture was stirred forminutes. The heat was then removed from the kettle and the reactionmixture cooled down to 200 F. with stirring. During the cooling period,0.34 pound of 49.3 per cent caustic solution amounting, on the basis ofsodium hydroxide added, to approximately 0.3 weight per cent of thefinal calculated grease composition, were added to the reaction mixtureat a temperature of approximately 275 to 300 F.; 0.57 pound ofdiphenylamine dissolved in 0.79 pound of 20 grade paraffmic minerallubricating oil was added at 250 F. The grease was drawn from the kettleat 200 F. and pumped through three -60 mesh screens into containers. Thesodium grease thus prepared had the following calculated composition:

Na 3:1 menhaden oil-Snodotte acid soap,

per cent 20.2

Excess NaOH in charge, per cent 1.9 Added later 0.3 Glycerin (from fat),per cent 1.5

Paraiiinic mineral oil, SAE 20, per cent--- 63.6

Aluminum stearate, per cent 5.0

Sodium petroleum mahogany sul'fonate, per

cent 1.5

Diphenylamine, per cent 1.0

D. C. Anti-Foam A, parts per million 220 The properties of the greasethus prepared are as follows:

Emmple I I A lithium base grease was prepared in accordance with theprocedure set forth for sodium base grease in Example I. The proportionsof reactants and the reaction conditions were exactly the same as thoseset forth in Example I. Neutralization of soap-forming constituents andexcess alkali was supplied by 22.1 pounds of 10.2 per cent lithiumhydroxide solution; 20.5 pounds were 6 added prior to saponification and1.6 pounds during the cooling of the grease. The lithium grease thusprepared had the following calculated composition:

Li 3:1 menhaden oil-Snodotte acid soap,

per cent 20.2

Excess alkali in charge 1.9

Added later 0.3 Glycerin 1.5 Paraffinic mineral oil SAE 20'. 68.6Aluminum stearate 5.0 Sodium petroleum mahogany su1fonate 1.5Diphenylamine 1.0 D. C. Anti-Foam A, parts per million 220 Theproperties of the lithium base grease thus prepared are as follows:

The foregoing examples illustrate the excellent wide temperature rangeball and roller bearing alkali metal greases that can be prepared by theprocess of this invention. The high dropping points and the good lowtemperature torque properties are particularly significant. The processof the invention is an important step forward in the art of greasemaking since it provides for the first time a preparative procedure foralkali metal greases which can be classified as wide temperature rangeball and roller bearing greases.

Obviously, many modifications and variations of the invention ashereinbefore set forth may be made without departing from the spirit andscope thereof and, therefore, only such limitations should be imposed asare indicated in the appended claims.

We claim:

1. A process for preparing alkali metal greases which comprisessaponifying a mixture of a mineral lubricating oil fraction, an aqueoussolution of alkali metal hydroxide and a soap-forming material selectedfrom the group consisting of soap-forming acids, soap-forming esters andmixtures thereof, said alkali metal hydroxide being in excess of thestoichiometric amount required for saponification of said soap-formingmaterial, dehydrating said mixture and digesting said saponified anddehydrated reaction mass at an elevated temperature of 300 to 390 F., atan air pressure of 50 to 120 pounds per square inch for a period of atleast five hours, cooling and drawing said reaction mixture.

2. A process according to claim 1 in which digestion of the saponified,dehydrated reaction rgrixture is effected at a temperature of 340 to 3.A process according to claim 1 in which the digestion of the reactionmixture is effected at a pressure between 70 and pounds per square inch.

4. A process according to claim 1 in which the soap-forming material hasan iodine number of at least 40.

A process according to claim 1 in which a saturated aqueous solution ofsodium hydroxide is employed.

6. A process according to claim 1 in which a saturated aqueous solutionof lithium hydroxide is employed.

7. A process according to claim 1 in which the excess alkali metalhydroxide amounts to approximately 1 to 3 per cent of the finalcalculated grease composition.

8. A process for preparing alkali metal greases which comprisessaponifying a mixture of a mineral lubricating oil fraction, an olefinicsoapforming material having an iodine number higher than and selectedfrom the group consisting of soap-forming acids, soap-forming esters andmixtures thereof, and an aqueous solution of alkali metal hydroxide,said alkali metal hydroxide being in excess of the stoichiometric amountrequired to saponify said soap-forming material, dehydrating saidmixture and digestme said saponified and dehydrated reaction mass at anelevated temperature of 300 to 390 F. at anelevated pressure of to 120p. s. i. g. for a period of at least 5 hours, cooling and drawing saidreaction mixture.

9. A process according to claim 8 in which digestion of the saponifieddehydrated reaction mixture is effected at a temperature of 340 to 365F.

10. A process according to claim 8 in which digestion of 'the reactionmixture is effected at a pressure between and p. s. i. g.

11. A process according to claim 8 in which said olefinic soap-formingmaterial has an iodine number higher than 90.

12. A process according to claim 8 in which the excess alkali metalhydroxide is approximately 1 to 3 per cent of the final calculatedgrease composition.

JOHN P. DILWORTH. GEORGE W. ECKERT. WELIAM J. COPPOC.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number 7 Name Date 1,971,750 Kaufman Aug. 28, 19342,084,974 Kaufman June 22, 1937 2,189,661 Buford Feb. 6, 1940 2,374,913Beerbower et al May 1, 1945 2,417,728 McLennan Mar. 18, 1947 2,428,123Morgan et al Sept. 30, 1947 2,495,651 Butcosk Jan. 24, 1950

1. A PROCESS FOR PREPARING ALAKLI METAL GREASES WHICH COMPRISESSAPONIFYING A MIXTURE OF A MINERAL LUBRICATING OIL FRACTION, AN AQUEOUSSOLUTION OF ALKALI METAL HYDROXIDE AND A SOAP-FORMING MATERIAL SELECTEDFROM THE GROUP CONSISTING OF SOAP-FORMING ACIDS, SOAP-FORMING ESTERS ANDMIXTURES THEREOF, SAID ALKALI METAL HYDROXIDE BEING IN EXCESS OF THESTOICHIOMETRIC AMOUNT REQUIRED FOR SAPONIFICATION OF SAID SOAP-FORMINGMATERIAL, DEHYDRATING SAID MIXTURE AND DIGESTING SAID SAPONIFIED ANDDEHYDRATED REACTION MASS AT AN ELEVATED TEMPERATURE OF 300 TO 390* F.,AT AN AIR PRESSURE OF 50 TO 120 POUNDS PER SQUARE INCH FOR A PERIOD OFAT LEAST FIVE HOURS, COOLING AND DRAWING SAID REACTION MIXTURE.